CN113564451B - Preparation method and application of high-contact fatigue resistance austempered ductile iron - Google Patents
Preparation method and application of high-contact fatigue resistance austempered ductile iron Download PDFInfo
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- CN113564451B CN113564451B CN202110744831.XA CN202110744831A CN113564451B CN 113564451 B CN113564451 B CN 113564451B CN 202110744831 A CN202110744831 A CN 202110744831A CN 113564451 B CN113564451 B CN 113564451B
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/08—Making cast-iron alloys
- C22C33/10—Making cast-iron alloys including procedures for adding magnesium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D5/00—Heat treatments of cast-iron
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/04—Cast-iron alloys containing spheroidal graphite
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Abstract
The invention relates to the field of preparation of nodular cast iron, and relates to a preparation method and application of high-contact fatigue resistance austempered ductile iron. The preparation method of the austempered ductile iron comprises the following steps: (1) preparing the nodular cast iron by adopting a punching method and a multiple inoculation method; (2) and (2) sequentially carrying out austenitizing, primary isothermal quenching, secondary isothermal quenching and low-temperature tempering on the nodular cast iron obtained in the step (1) to finally obtain the austempered ductile iron. The austempered ductile iron obtained by the method has higher contact fatigue resistance and contact fatigue life; the dissolution of the carburant can be promoted, and the size and distribution of the ink in the finished product tissue are more uniform; can be applied to gears, crankshaft connecting rods and crank connecting rods, and enables the gears, the crankshaft connecting rods and the crank connecting rods to be thin-walled and light.
Description
Technical Field
The invention relates to the field of preparation of nodular cast iron, and particularly relates to a preparation method and application of novel high-contact fatigue resistance austempered ductile iron.
Background
Austempered ductile iron is originally obtained from ductile iron under austempering conditions and is therefore also referred to as austempered ductile iron. The unique ausferrite structure comprises acicular ferrite and carbon-rich austenite. Compared with the traditional steel materials, the austempered ductile iron has higher specific strength, impact toughness, fracture toughness and wear resistance, and is widely applied to automobile parts such as gears, crankshafts, chain wheels and the like, common wear-resistant parts and important structural parts with high performance and high precision requirements.
With the rapid development of the fields of automobiles, agricultural machinery, infrastructure construction and the like, higher requirements are put forward on the mechanical properties of the austempered ductile iron, and new challenges are also put forward on the heat treatment process of the austempered ductile iron. In the automobile manufacturing industry, as for gears and crankshafts produced by using austempered ductile iron, the service conditions have the characteristics of high local stress, high relative movement speed and the like, and rolling contact fatigue damage is one of the main reasons of failure of the gears and crankshafts, however, most of the current methods control blank quality, add alloy elements and other methods, and in the process of preparing ductile cast iron, a carburant floats upwards and is difficult to be fully dissolved in molten iron, so that the rolling contact fatigue resistance of the austempered ductile iron is difficult to further improve.
The authorization number CN110295265B discloses austempered ductile iron and a preparation method and application thereof, wherein the austempered ductile iron comprises the following elements in percentage by mass: 3.35 to 3.44 percent of C, 2.37 to 2.45 percent of Si, 0.21 to 0.23 percent of Mn, 1.02 to 1.26 percent of Ni, 0.69 to 0.8 percent of Cu, 0.17 to 0.32 percent of Mo, 0.05 to 0.07 percent of Mg, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and the balance of Fe. The preparation method comprises the following steps: a. mixing and smelting pig iron, scrap steel, foundry returns, carburant, silicon carbide and silicon at the smelting temperature of 1500-; b. adding a primary inoculant, a nodulizer and a covering agent into the bag, tamping, and then pouring iron liquid into the bag; removing slag; pouring the mixture into a ladle for secondary inoculation, and adding a secondary inoculant; removing slag; casting to obtain a casting, and adding a tertiary inoculant along with the flow during casting; c. and (5) carrying out isothermal quenching treatment.
No. CN107723583B discloses a high-performance as-cast austempered ductile iron and a production method and application thereof. The invention is based on the casting of a nodular cast iron shell mold, limits the adding amount range of bainite forming elements Mo, Ni and Cu according to the casting size and the shelling time, and finally determines the cast-state austempered ductile iron production method suitable for complex shape characteristics by finely controlling the shelling time, the cooling and the heat preservation process.
Disclosure of Invention
In order to solve the problems, the invention provides a preparation method of novel austempered ductile iron with high contact fatigue resistance, which has higher contact fatigue resistance and contact fatigue life; the size of the nodular graphite is easy to control, and the nodular graphite is uniformly distributed.
The specific invention content is as follows: a preparation method of novel austempered ductile iron with high contact fatigue resistance comprises the following steps:
(1) preparing nodular cast iron:
1a, smelting raw materials to obtain molten iron, standing to remove slag, adding a carburant, and then pouring the molten iron into a preheating ladle pit paved with a nodulizer and a primary inoculant;
1b, standing the molten iron in the ladle pit for deslagging, pouring after the liquid level is calm, adding a secondary inoculant along with the flow in the pouring process, and then naturally cooling to room temperature to obtain nodular cast iron;
(2) preparing novel austempered ductile iron:
2a, heating the nodular cast iron obtained in the step (1) to 900-;
2b, performing primary isothermal quenching on the austenitized nodular cast iron within 1min, wherein the isothermal temperature is 260-280 ℃, and the heat preservation time is 2-3 min;
2c, performing secondary isothermal quenching on the nodular cast iron subjected to primary isothermal quenching within 1min, wherein the isothermal temperature is 380-400 ℃, the heat preservation time is 60-70min, and then air-cooling to room temperature to obtain an austempered ductile iron crude product;
2d, tempering the crude austempered ductile iron product obtained in the step 2c at the temperature of 280-300 ℃ for 25-30min, and then cooling the crude austempered ductile iron product to room temperature in air to finally obtain a novel finished austempered ductile iron product.
According to the technical scheme, the carburant and the inoculant are added step by step in the preparation of the nodular cast iron, so that the carbon content is controlled, and the nodular graphite is more uniform. During the specific operation, a medium frequency induction furnace is adopted to smelt the nodular cast iron raw material at the temperature of 1560-1580 ℃ to obtain molten iron, the molten iron is kept stand to remove slag, slag is mainly introduced by impurities in the raw material, a carburant is added, then a nodulizer and an inoculant are added when the slag is poured into a ladle pit, and the nodulizer and the inoculant are paved at the bottom of the ladle pit in advance so as to be capable of stirring the nodulizer and the inoculant into the molten iron when the slag is poured. And (5) removing the residual slag in the step 1b to ensure the product quality. After the nodular cast iron is obtained, the nodular cast iron is placed into a high-temperature salt bath furnace, the temperature is raised to 900-plus-one temperature of 920 ℃, austenitizing treatment is carried out on the nodular cast iron, the nodular cast iron is transferred into a low-temperature salt bath furnace for first-stage isothermal quenching treatment after heat preservation for 80-100min, the nodular cast iron is taken out after heat preservation for 2-3min, at the moment, a large amount of lower bainite forms nuclei, the nodular cast iron is transferred into a medium-temperature salt bath furnace for second-stage isothermal quenching treatment in 1min, carbon atoms can be rapidly diffused in the process, the growth of the lower bainite of the nuclei in the first-stage isothermal quenching treatment is promoted, and a uniform lower bainite tissue is formed. Taking out the product, air-cooling to room temperature, then placing the product into a box furnace for low-temperature tempering at the temperature of 380-400 ℃, keeping the temperature for 60-70min, and finally air-cooling to room temperature to obtain the austempered ductile iron. The element components in the austempered ductile iron are adjusted and controlled by controlling the mass fraction of the additive.
Preferably, the step of adding the carburant in the step (1) is as follows:
A. embedding the tungsten carbide carrier into a container filled with the recarburizer powder, and oscillating the container to enable the tungsten carbide powder to be loaded in small holes on the surface of the tungsten carbide carrier;
B. b, putting the tungsten carbide carrier loaded with the carburant obtained in the step A into the molten iron in the step 1a, standing, and then performing ultrasonic oscillation and standing;
C. and after molten iron is poured into the ladle pit, taking out the tungsten carbide carrier, cooling the tungsten carbide carrier, placing the tungsten carbide carrier into a sulfuric acid solution, and taking out the tungsten carbide carrier after iron attached to the surface of the tungsten carbide carrier is dissolved.
Considering that the tungsten carbide is insoluble in molten iron, has density higher than that of the molten iron, has good wettability with the molten iron, has melting point higher than the temperature of the molten iron, and can increase the wear resistance of the cast iron by a small amount of the fused tungsten element. Therefore, the invention uses the carbon-containing composite material as a carrier of the recarburizing agent and is used for solving the problem of floating of the recarburizing agent. According to the invention, the recarburizer is filled in the tungsten carbide carrier, when the tungsten carbide carrier filled with the recarburizer is placed in molten iron, the tungsten carbide carrier sinks, in the process, the molten iron and the surface of the tungsten carbide have good wettability, the molten iron is also filled in the tungsten carbide carrier, and in the process, the recarburizer in the small hole of the tungsten carbide carrier can float out of the molten iron as the molten iron permeates into the small hole loaded with the recarburizer. The standing before the ultrasonic treatment is to enable the tungsten carbide carrier to fully sink, and the ultrasonic treatment mainly has two functions, one is to enable the carburant in the tungsten carbide carrier to be diffused into molten iron as much as possible, and the other is to enable the carburant to be uniformly distributed in the carrier as much as possible. And pouring molten iron into the ladle pit, taking out the tungsten carbide carrier, cooling and placing the tungsten carbide carrier into a sulfuric acid solution. Since tungsten carbide is insoluble in a sulfuric acid solution, iron filled in the tungsten carbide carrier can be removed in the sulfuric acid solution, so that tungsten carbide can be recycled.
Preferably, the recarburizer in the step A is carbon powder with the purity of more than 99%, the particle size of the carbon powder is less than 10 microns, the nitrogen content is less than 0.03%, the sulfur content is less than 0.02%, and the adding amount of the carbon powder in molten iron is 0.1-1.0 wt%.
The carburant adopted by the invention is carbon powder with the purity of more than 99 percent, and in order to ensure that the carbon powder is uniformly distributed in molten iron and can be better filled in a tungsten carbide carrier, the particle size of the carbon powder used by the invention is less than 10 mu m. Since P and S are detrimental to the performance of austempered ductile iron, the composition of these two elements in the amount of the recarburizer is strictly controlled.
Preferably, in the step (1), the particle size of the tungsten carbide carrier in the step A is 3-5 cm; the tungsten carbide carrier is provided with small holes uniformly distributed on the surface; the aperture of the small hole is less than 2mm, and the depth is less than 5 mm.
In order to uniformly disperse the recarburizer, the particle size of the tungsten carbide carrier selected by the invention is 3-5cm, the surface of the tungsten carbide carrier is provided with uniformly distributed pores for filling the recarburizer, the pore diameter and the depth of the pores are not too large, and the recarburizer is prevented from floating out too early, so that the pore diameter of the pores is less than 2mm, and the depth of the pores is less than 5 mm.
Preferably, in the step (1), the nodulizer in the step 1a is 1.3-1.7wt% of rare earth magnesium, and the particle size is 10-30 mm; in the step (1), the primary inoculant in the step 1a is 0.4-0.6wt% of 75 ferrosilicon, and the granularity is 5-10 mm; 1c the secondary inoculant is 0.15-0.25wt% of 75 ferrosilicon, and the granularity is 1-3 mm.
The rare earth is added with purified molten iron, so that stress concentration is reduced, the fatigue crack initiation effect is reduced, in order to refine the spheroidal graphite and enable the spheroidal graphite to be uniformly dispersed in the austempered ductile iron, the grain diameter of the added nodulizer and the inoculant is strictly controlled, and meanwhile, the grain diameter of the secondary inoculant is smaller than that of the primary inoculant.
Preferably, in the step (2), the first-stage isothermal quenching of 2b is salt bath isothermal quenching, and the salt bath medium is KNO with the mass ratio of 0.9-1.1:13And NaNO3(ii) a Austenitized ductile iron is subjected to primary austempering within 20S.
Preferably, in the step (2), the second-stage isothermal quenching of 2c is salt bath isothermal quenching, and the salt bath medium is KCl, NaCl and CaCl with the mass ratio of 4.5-5.5:1.5-2.5:2.5-3.52(ii) a And carrying out secondary isothermal quenching on the nodular cast iron obtained in the step 2b in 20S.
KNO3And NaNO3The high-temperature salt bath can generate nitrite by adopting KCl, NaCl and CaCl2Can avoid the problem and is environment-friendly.
Preferably, in the step (2), the 2c step of obtaining the austempered ductile iron rough product is carried out for 2d within 1 h.
There is a certain residual stress in the austempered ductile iron raw product obtained by 2c and a tempering treatment in a shorter time is required due to the presence of austenite, otherwise the surface is liable to develop micro-crack nucleation.
Secondly, the invention provides the novel high-contact fatigue resistance austempered ductile iron prepared by the method, which comprises the following components: 3.50 to 3.60 weight percent of C, 2.20 to 2.40 weight percent of Si, 0.16 to 0.17 weight percent of Mn, less than or equal to 0.05 weight percent of P, less than or equal to 0.05 weight percent of S, 0.01 to 0.03 weight percent of Mo, 0.04 to 0.06 weight percent of Ni, 0.70 to 0.80 weight percent of Cu, 0.04 to 0.06 weight percent of Mg, 0.03 to 0.05 weight percent of Cr and the balance of iron.
In the invention, C is the key of graphite formation in the austempered ductile iron, and the carbon content can enhance the fluidity of molten iron and improve the component uniformity and performance stability of a final product in a proper range. The quantity of the nodular graphite and the ferrite can be controlled by Si, and in the invention, the mass percentage content of Si is strictly controlled to be 2.20-2.40wt%, so that a proper quantity distribution of the nodular graphite is obtained. Mn can refine pearlite and improve strength and hardness, but Mn is not suitable for being excessively high in austempered ductile iron, so that the mass percentage of Mn is controlled to be 0.16-0.17 wt%. The presence of Mg facilitates spheroidization.
In addition, the invention also provides an application method of the austempered ductile iron, which is used for preparing gears, crankshafts and chain wheels.
The invention has the beneficial effects that:
1. the rolling contact fatigue resistance and the fatigue life of the prepared austempered ductile iron are obviously improved;
2. the dissolution of the carburant can be promoted, and the size and distribution of the ink in the finished product tissue are more uniform;
3. the method is applied to gears, crankshaft connecting rods and crank connecting rods, and enables the gears, the crankshaft connecting rods and the crank connecting rods to be thin-walled and light.
Drawings
FIG. 1 is a schematic diagram of the heat treatment process of austempered ductile iron of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples. The devices, reagents and methods referred to in the present invention are those known in the art unless otherwise specified.
FIG. 1 is a schematic diagram showing the heat treatment process of austenitizing the prepared nodular cast iron at 920 ℃ of 900-.
Example 1
The preparation method of austempered ductile iron of the embodiment comprises the following steps:
(1) preparing nodular cast iron:
1a, smelting raw materials to obtain molten iron, standing for deslagging, placing a plurality of tungsten carbide carriers with the diameter of 5cm into the molten iron, filling 0.5 wt% of carbon powder into small holes on the surface of the tungsten carbide, standing for one minute, then ultrasonically oscillating for 10min, and pouring the molten iron into a preheating ladle pit paved with a nodulizer and a primary inoculant after the completion;
1b, standing the molten iron in the ladle pit for deslagging, pouring after the liquid level is calm, adding a secondary inoculant along with the flow in the pouring process, and then naturally cooling to room temperature to obtain nodular cast iron;
(2) preparing austempered ductile iron:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 260 ℃, and the heat preservation time is 2 min;
transferring the nodular cast iron into a medium-temperature salt bath furnace for secondary isothermal quenching in 2c.20S, wherein the isothermal temperature is 380 ℃, the heat preservation time is 60min, taking out the nodular cast iron, and cooling to room temperature;
and 2d, putting the cooled nodular cast iron into a box furnace for low-temperature tempering after 30min, wherein the tempering temperature is 280 ℃, the tempering time is 25min, and then air-cooling to room temperature to finally obtain the novel austempered ductile iron.
Example 2
(1) Preparing nodular cast iron: same as example 1;
(2) preparing austempered ductile iron:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 260 ℃, and the heat preservation time is 2 min;
transferring the nodular cast iron into a medium-temperature salt bath furnace for secondary isothermal quenching in 2c.20S, wherein the isothermal temperature is 400 ℃, the heat preservation time is 60min, taking out the nodular cast iron, and cooling to room temperature;
and 2d, putting the cooled nodular cast iron into a box furnace for low-temperature tempering after 30min, wherein the tempering temperature is 280 ℃, the tempering time is 25min, and then air-cooling to room temperature to finally obtain the novel austempered ductile iron.
Example 3
(1) Preparing nodular cast iron: same as example 1;
(2) preparing austempered ductile iron:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 280 ℃, and the heat preservation time is 2 min;
transferring the nodular cast iron in 2c.20S into a medium-temperature salt bath furnace for secondary isothermal quenching, wherein the isothermal temperature is 380 ℃, the heat preservation time is 60min, taking out the nodular cast iron, and cooling to room temperature;
and 2d, putting the cooled nodular cast iron into a box furnace for low-temperature tempering after 30min, wherein the tempering temperature is 280 ℃, the tempering time is 25min, and then air-cooling to room temperature to finally obtain the novel austempered ductile iron.
Example 4
(1) Preparing nodular cast iron: same as example 1;
(2) preparing austempered ductile iron:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 260 ℃, and the heat preservation time is 2 min;
transferring the nodular cast iron into a medium-temperature salt bath furnace for secondary isothermal quenching in 2c.20S, wherein the isothermal temperature is 380 ℃, the heat preservation time is 60min, taking out the nodular cast iron, and cooling to room temperature;
and 2d, putting the cooled nodular cast iron into a box furnace for low-temperature tempering after 30min, wherein the tempering temperature is 300 ℃, the tempering time is 25min, and then air-cooling to room temperature to finally obtain the novel austempered ductile iron.
Example 5
(1) Preparing nodular cast iron: same as example 1;
(2) preparing austempered ductile iron:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 260 ℃, and the heat preservation time is 3 min;
transferring the nodular cast iron into a medium-temperature salt bath furnace for secondary isothermal quenching in 2c.20S, wherein the isothermal temperature is 380 ℃, the heat preservation time is 60min, taking out the nodular cast iron, and cooling to room temperature;
and 2d, putting the cooled nodular cast iron into a box furnace for low-temperature tempering after 30min, wherein the tempering temperature is 280 ℃, the tempering time is 25min, and then air-cooling to room temperature to finally obtain the novel austempered ductile iron.
Example 6
(1) Preparing nodular cast iron: same as example 1;
(2) preparing austempered ductile iron:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 260 ℃, and the heat preservation time is 2 min;
transferring the nodular cast iron into a medium-temperature salt bath furnace for secondary isothermal quenching in 2c.20S, wherein the isothermal temperature is 380 ℃, the heat preservation time is 70min, taking out the nodular cast iron, and cooling to room temperature;
and 2d, putting the cooled nodular cast iron into a box furnace for low-temperature tempering after 30min, wherein the tempering temperature is 280 ℃, the tempering time is 25min, and then air-cooling to room temperature to finally obtain the novel austempered ductile iron.
Example 7
(1) Preparing nodular cast iron: same as example 1;
(2) preparing austempered ductile iron:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 260 ℃, and the heat preservation time is 2 min;
transferring the nodular cast iron into a medium-temperature salt bath furnace for secondary isothermal quenching in 2c.20S, wherein the isothermal temperature is 380 ℃, the heat preservation time is 60min, taking out the nodular cast iron, and cooling to room temperature;
and 2d, putting the cooled nodular cast iron into a box furnace for low-temperature tempering after 30min, wherein the tempering temperature is 280 ℃, the tempering time is 30min, and then air-cooling to room temperature to finally obtain the novel austempered ductile iron.
Example 8
(1) Preparing nodular cast iron:
1a, smelting raw materials to obtain molten iron, standing for deslagging, placing a plurality of tungsten carbide carriers with the diameter of 5cm into the molten iron, filling 1.0wt% of carbon powder into small holes on the surface of the tungsten carbide, standing for one minute, then ultrasonically oscillating for 10min, and pouring the molten iron into a preheating ladle pit paved with a nodulizer and a primary inoculant after the completion;
1b, standing the molten iron in the ladle pit for deslagging, pouring after the liquid level is calm, adding a secondary inoculant along with the flow in the pouring process, and then naturally cooling to room temperature to obtain nodular cast iron;
(2) preparing austempered ductile iron: same as in example 1.
Example 9
(1) Preparing nodular cast iron:
1a, smelting raw materials to obtain molten iron, standing for deslagging, adding 0.5 wt% of carbon powder, and then pouring the molten iron into a preheating ladle pit paved with a nodulizer and a primary inoculant;
1b, standing the molten iron in the ladle pit for deslagging, pouring after the liquid level is calm, adding a secondary inoculant along with the flow in the pouring process, and then naturally cooling to room temperature to obtain nodular cast iron;
(2) preparing austempered ductile iron: same as in example 1.
Comparative example 1
Preparing nodular cast iron: same as example 1;
isothermal quenching was not performed.
Comparative example 2
(1) Preparing nodular cast iron: same as example 1;
(2) preparing austempering for the first time:
austenitizing the nodular cast iron obtained in the step (1) at 900 ℃ by using a high-temperature salt bath furnace, and keeping the temperature for 80 min;
and 2b.20S, transferring the austenitized nodular cast iron into a low-temperature salt bath furnace for primary isothermal quenching, wherein the isothermal temperature is 380 ℃, and the heat preservation time is 60 min.
Performance testing
The ball-disk rotational rolling contact fatigue test was performed using a UMT-3 multifunctional frictional wear tester, and the results are shown in Table 1.
TABLE 1
| Serial number | Rolling contact fatigue life (min) |
| Example 1 | 981 |
| Example 2 | 950 |
| Example 3 | 973 |
| Example 4 | 934 |
| Example 5 | 985 |
| Example 6 | 938 |
| Example 7 | 921 |
| Example 8 | 984 |
| Example 9 | 853 |
| Comparative example 1 | 641 |
| Comparative example 2 | 778 |
The results of comparative examples 1 to 9 and comparative examples 1 to 2 show that the heat treatment process of the invention of the step austempering plus tempering has a better acceleration effect on the fatigue life relief of the austempered ductile iron. The reason for this is probably that in the staged isothermal quenching process of the invention, the first-stage isothermal quenching generates a large amount of lower bainite nucleation, the lower bainite has better mechanical property, in the second-stage isothermal quenching process, carbon atoms are uniformly diffused in the austempered ductile iron, the lower bainite grows, the tempering process eliminates surface stress, promotes the further homogenization of the structure, and simultaneously eliminates the nucleation of microcracks. The difference in results between the results of examples 1 to 8 is that the conditions of examples 4,6 and 7 resulted in a larger structure, and examples 1 to 8 differed from example 9 in that the carburant was not loaded with tungsten carbide, resulting in partial floating of the carburant, affecting the carbon content of the actual final product.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.
Claims (9)
1. The preparation method of the high contact fatigue resistance austempered ductile iron is characterized by comprising the following steps:
(1) preparing nodular cast iron:
1a, smelting raw materials to obtain molten iron, standing to remove slag, adding a carburant, and then pouring the molten iron into a preheating ladle pit paved with a nodulizer and a primary inoculant;
1b, standing the molten iron in the ladle pit for deslagging, pouring after the liquid level is calm, adding a secondary inoculant along with the flow in the pouring process, and then naturally cooling to room temperature to obtain nodular cast iron;
(2) preparing austempered ductile iron:
2a, heating the nodular cast iron obtained in the step (1) to 900-;
2b, performing primary isothermal quenching on the austenitized nodular cast iron within 1min, wherein the isothermal temperature is 260-280 ℃, and the heat preservation time is 2-3 min;
2c, performing secondary isothermal quenching on the nodular cast iron subjected to primary isothermal quenching within 1min, wherein the isothermal temperature is 380-400 ℃, the heat preservation time is 60-70min, and then air-cooling to room temperature to obtain an austempered ductile iron crude product;
2d, tempering the crude austempered ductile iron product obtained in the step 2c at the temperature of 280-300 ℃ for 25-30min, and then air-cooling to room temperature to finally obtain a novel finished austempered ductile iron product;
the step (1) of adding the carburant comprises the following steps:
A. embedding the tungsten carbide carrier into a container filled with the recarburizer powder, and oscillating the container to enable the tungsten carbide powder to be loaded in small holes on the surface of the tungsten carbide carrier;
B. b, putting the tungsten carbide carrier loaded with the carburant obtained in the step A into the molten iron in the step 1a, standing, and then performing ultrasonic oscillation and standing;
C. and after molten iron is poured into the ladle pit, taking out the tungsten carbide carrier, cooling the tungsten carbide carrier, placing the tungsten carbide carrier into a sulfuric acid solution, and taking out the tungsten carbide carrier after iron attached to the surface of the tungsten carbide carrier is dissolved.
2. The preparation method according to claim 1, wherein the recarburizer in the step A is carbon powder with a purity of 99%, the particle size of the carbon powder is less than 10 μm, the nitrogen content is less than 0.03%, the sulfur content is less than 0.02%, and the addition amount of the carbon powder in the molten iron is 0.1-1.0 wt%.
3. The method according to claim 1, wherein the particle size of the tungsten carbide support in the step a is 3 to 5 cm; the tungsten carbide carrier is provided with small holes uniformly distributed on the surface; the aperture of the small hole is less than 2mm, and the depth is less than 5 mm.
4. The method according to claim 1, wherein in the step (1), the nodulizer of 1a is 1.3-1.7wt% of rare earth magnesium and has a particle size of 10-30 mm; in the step (1), the primary inoculant in the step 1a is 0.4-0.6wt% of 75 ferrosilicon, and the granularity is 5-10 mm; 1c the secondary inoculant is 0.15-0.25wt% of 75 ferrosilicon, and the granularity is 1-3 mm.
5. The preparation method according to claim 1, wherein in the step (2), the first-stage austempering of 2b is salt bath austempering, and the salt bath medium comprises KNO3 and NaNO3 in a mass ratio of 0.9-1.1: 1; austenitized ductile iron is subjected to primary austempering within 20S.
6. The preparation method of claim 1, wherein in step (2), the second-stage austempering of 2c is salt bath austempering, and the salt bath medium is KCl, NaCl and CaCl2 in a mass ratio of 4.5-5.5:1.5-2.5: 2.5-3.5; and carrying out secondary isothermal quenching on the nodular cast iron obtained in the step 2b in 20S.
7. The method according to claim 1, wherein in the step (2), the 2c step of obtaining the austempered ductile iron rough product is performed within 1h for 2d of the tempering process.
8. An austempered ductile iron having high contact fatigue resistance prepared by the preparation method according to any one of claims 1 to 7, wherein the austempered ductile iron comprises the following components: 3.50 to 3.60 weight percent of C, 2.20 to 2.40 weight percent of Si, 0.16 to 0.17 weight percent of Mn, less than or equal to 0.05 weight percent of P, less than or equal to 0.05 weight percent of S, 0.01 to 0.03 weight percent of Mo, 0.04 to 0.06 weight percent of Ni, 0.70 to 0.80 weight percent of Cu, 0.04 to 0.06 weight percent of Mg, 0.03 to 0.05 weight percent of Cr and the balance of iron.
9. Use of the austempered ductile iron of claim 8 in the manufacture of gears, crankshafts, or sprockets.
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